Causes of the Arctic’s Lower-Tropospheric Warming Structure

Arctic amplification has been attributed predominantly to a positive lapse rate feedback in winter, when boundary-layer temperature inversions focus warming near the surface. Predicting high-latitude climate change effectively thus requires identifying the local and remote physical processes that set the Arctic’s vertical warming structure. In this study, we analyze output from the CESM Large Ensemble’s 21st century climate change projection to diagnose the relative influence of two Arctic heating sources, local sea-ice loss and remote changes in atmospheric heat transport. Causal effects are quantified with a statistical inference method, allowing us to assess the energetic pathways mediating the Arctic temperature response and the role of internal variability across the ensemble. We find that a step-increase in latent heat flux convergence causes Arctic lower-tropospheric warming in all seasons, while additionally reducing net longwave cooling at the surface. However, these effects only lead to small and short-lived changes in boundary layer inversion strength. By contrast, a step-decrease in sea-ice extent in the melt season causes, in fall and winter, surface-amplified warming and weakened boundary-layer temperature inversions. Sea-ice loss also enhances surface turbulent heat fluxes and cloud-driven condensational heating, which mediate the atmospheric temperature response. While the aggregate effect of many moist transport events and seasons of sea-ice loss will be different than the response to hypothetical perturbations, our results nonetheless highlight the mechanisms that alter the Arctic temperature inversion in response to CO2 forcing. As sea ice declines, the atmosphere’s boundary-layer temperature structure is weakened, static stability decreases, and a thermodynamic coupling emerges between the Arctic surface and the overlying troposphere.

Causes of the Arctic's Lower-Tropospheric Warming Structure

Arctic amplification has been attributed predominantly to a positive lapse rate feedback in winter, when boundary-layer temperature inversions focus warming near the surface. Predicting high-latitude climate change effectively thus requires identifying the local and remote physical processes that set the Arctic’s vertical warming structure. In this study, we analyze output from the CESM Large Ensemble's 21st century climate change projection to diagnose the relative influence of two Arctic heating sources, local sea-ice loss and remote changes in atmospheric heat transport. Causal effects are quantified with a statistical inference method, allowing us to assess the energetic pathways mediating the Arctic temperature response and the role of internal variability across the ensemble. We find that a step-increase in latent heat flux convergence causes Arctic lower-tropospheric warming in all seasons, while additionally reducing net longwave cooling at the surface. However, these effects only lead to small and short-lived changes in boundary layer inversion strength. By contrast, a step-decrease in sea-ice extent in the melt season causes, in fall and winter, surface-amplified warming and weakened boundary-layer temperature inversions. Sea-ice loss also enhances surface turbulent heat fluxes and cloud-driven condensational heating, which mediate the atmospheric temperature response. While the aggregate effect of many moist transport events and seasons of sea-ice loss will be different than the response to hypothetical perturbations, our results nonetheless highlight the mechanisms that alter the Arctic temperature inversion in response to CO2 forcing. As sea ice declines, the atmosphere’s boundary-layer temperature structure is weakened, static stability decreases, and a thermodynamic coupling emerges between the Arctic surface and the overlying troposphere.

DYNAMIC RESPONSE OF PHOTOPOLYMER RESINS CORES FOR NAVAL APPLICATIONS IN EXTREME ENVIRONMENTS

Due to the melting of polar ice caps, large deposits of natural resources are becoming more readily available, leading to an increase in arctic naval exploration. Naval vessels and ship hulls must be built with lightweight structures, such as sandwich composites, to increase the ship’s fuel efficiency. However, identifying new material choices that can withstand the harsh Arctic environments is crucial for the survivability and safety of personnel and structures. This study investigates the potential of photopolymer resins through additive manufacturing as a lightweight sandwich composite core material. The thermo-mechanical properties of this resin were evaluated using: tensile, flexural, and compressive tests according to the ASTM Standards D638, D695, and D790, respectively. Tests were conducted at room temperature (23 C) and arctic temperature (-60 C). The experimental data will be used as an input for high-fidelity finite element (FE) simulations with the software ABAQUS. From the performed tests, the photopolymer exhibited isotropic behavior at both room (RT) and Arctic temperatures. Preliminary quasi-static results for “Durable Resin” at AT showed an increase of ~300% in its tensile, flexural, and compressive modulus and an increase of ~300% in its tensile and flexural strength and ~100% in its compressive strength when compared to the same resin at RT. The finite element analysis models showed good agreement with the experimental results. Zackery Nieto, The University of Texas at El Paso, 500 W. University Ave, El Paso,

Synoptic climatological approach associated with three recent summer heatwaves in the Canadian Arctic

The observed unusually high temperatures in the Arctic during recent decades can be related to the Arctic sea ice declines in summer 2007, 2012 and 2016. Arctic dipole formation has been associated with all three heatwaves of 2007, 2012 and 2016 in the Canadian Arctic. Here, the differences in weather patterns are investigated and compared with normal climatological mean (1981–2010) structures. This study examines the high-resolution datasets from the North American Regional Reanalysis model. During the study periods, the north of Alaska has been affected by the low-pressure tongue. The maximum difference between Greenland high-pressure centre and Alaska low-pressure tongue for the summers of 2012, 2016 and 2007 are 8 hPa, 7 hPa and 6 hPa, respectively, corresponding and matching to the maximum summer surface Canadian Arctic temperature records. During anomalous summer heatwaves, low-level wind, temperatures, total clouds (%) and downward radiation flux at the surface are dramatically changed. This study shows the surface albedo has been reduced over most parts of the Canadian Arctic Ocean during the mentioned heatwaves (∼5–40%), with a higher change (specifically in the eastern Canadian Arctic region) during summer 2012 in comparison with summer 2016 and summer 2007, agreeing with the maximum surface temperature and sea ice decline records.

Arctic Ocean Sea Ice Area Extent Cyclicity and Non-Stationarity

<p>Arctic sea ice is a key component of the Arctic hydrologic cycle. This cycle is connected to land and ocean temperature variations and Arctic snow cover variations, spatially and temporally. Arctic temperature variations from historical observations shows an early 20th century increase (i.e. warming), followed by a period of Arctic temperature decrease (i.e. cooling) since the 1940s, which was followed by another period of Arctic temperature increase since the 1970s that continues into the two decades of the 21st century. Evidence has been accumulating that Arctic sea ice extent can experience multi-decadal to centennial time scale variations as it is a component of the Arctic Geohydrological System. </p><p><br>We investigate the multi-satellite and sensor daily values of area extent of Arctic sea ice since SMMR on Nimbus 7 (1978) to AMSR2 on GCOM-W1 (2019). From the daily time series we use the first year-cycle as a wave-pattern to compare to all subsequent years-cycles through April 2020 (in progress), and constitute a derivative time series. In this time series we find the emergence of a multi-decadal cycle, showing a relative minimum during the period of 2007 to 2014, and subsequently rising. This may be related to an 80-year cycle (hypothesis). The Earth’s weather system is principally driven the solar radiation and its variations. If the multi-decadal cycle in Arctic sea ice area extent that we interpret continues, it may be linked physically to the Wolf-Gleissberg cycle, a factor in the variations of terrestrial cosmogenic isotopes, ocean sediment layering and glacial varves, ENSO and Aurora.</p><p>Our hypothesis and results give more evidence that the multi-decadal variation of Arctic sea ice area extent is controlled by natural physical processes of the Sun-Earth system. </p>

Interdecadal Connection between Arctic Temperature and Summer Precipitation over the Yangtze River Valley in the CMIP5 Historical Simulations

<p>This study assesses the ability of the Coupled Model Intercomparison Project phase 5 (CMIP5) simulations in capturing the interdecadal precipitation enhancement over the Yangtze River valley (YRV) and investigates the contributions of Arctic temperature and mid- to high-latitude warming to the interdecadal variability of the East Asian summer monsoon rainfall. Six CMIP5 historical simulations including models from the Canadian Centre for Climate Modeling and Analysis (CCCma), the Beijing Climate Center, the Max Planck Institute for Meteorology, the Meteorological Research Institute, the Met Office Hadley Centre, and NCAR are used. The NCEP–NCAR reanalysis and observed precipitation are also used for comparison.Among the sixCMIP5 simulations, only CCCma can approximately simulate the enhancement of interdecadal summer precipitation over the YRV in 1990–2005 relative to 1960–75; the various relationships between the summer precipitation and surface temperature (Ts), 850-hPa winds, and 500-hPa height field (H500); and the relationships between Ts and H500 determined using regression, correlation, and singular value decomposition (SVD) analyses. It is found that CCCma can reasonably simulate the interdecadal surface warming over the boreal mid- to high latitudes in winter, spring, and summer. The summer Baikal blocking anomaly is postulated to be the bridge that links the winter and spring surface warming over the mid- to high latitude and Arctic with the enhancement of summer precipitation over the YRV. Models that missed some or all of these relationships found in CCCma and the reanalysis failed to simulate the interdecadal enhancement of precipitation over the YRV. This points to the importance of Arctic and mid- to high-latitude processes on the interdecadal variability of the East Asian summer monsoon and the challenge for global climate models to correctly simulate the linkages.</p>